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10:17 PM Mon 20 Apr 2009 GMT
Chris Tibbs is a meteorologist with a long history of racing yachts that has included three Round the World Races: twice in the Whitbread and as Skipper in the BT Global Challenge. He is now mainly involved with advising yachts and weather routing for racing and cruising yachts.
He is the author of a number of weather books and regularly contributes in yachting magazines:
From Ilhabela to Charleston is a distance of around 4,850 nm and is the leg of the race where the competitors can expect the lightest average wind strength of the race and the warmest weather. However whilst the sailing may be largely through warm tropical waters tactically it is a testing leg and whenever sailing in the tropics squalls are likely to build and hit at any time of day or night. In addition there is the ITCZ or doldrums to contend with, and whilst some places to cross the ITCZ are better than others, there will be an element of luck involved.
With the southern hemisphere summer giving way to winter, there is a change in the weather and there is a chance that a cold front starting life well to the south will reach as far north as Ilhabela. This will help the fleet on its way with southerly winds and rain but it is more likely that between the start and Cape Frio, an area known for light wind, we will have to rely on the sea breeze to get the fleet on its way. With 190 miles to reach the headland and the trade winds beyond, it will not be possible to reach the stronger wind on the afternoon sea breeze so it is likely to be a slow first 24 hours until the trades are reached.
This should be near Cape Frio where another tactical decision needs to be made. To the north and east are where the trade winds will be found but there is also the south moving Brazil current that hugs the coast that needs to be crossed. The trade winds when they are found will be from a N to NE direction making for a hard beat up the Brazilian coast.
So there is a difficult decision to be made as to how far to go offshore on port tack once past Cape Frio to get into the stronger and more established trade winds. Cutting the corner may shorten the distance, but to the east the wind should be stronger and more veered. Close to the coast there is the adverse Brazil current and also the wind will be lighter. In addition small areas of low pressure may drift from the land over the sea making progress very hit and miss. The hard part is to know just how far offshore to go before tacking N. Starting ahead of the Portim?o Race the Volvo fleet leaving Rio had the same choices to make and quite surprisingly both the inshore boat and the furthest offshore boats gained and were 1st and 2nd as they reached past Salvador, but there was not much lateral separation within the fleet.
Once on starboard tack there should be a gradual lift until the boats are able to ease sheets as they progress north and the trades change from the NE to SE. However tack too early and risk the lighter wind and stronger adverse current, and it is a very painful tack back out to the east, but leave it too late and the extra distance is hard to regain. Choosing when to head north is crucial and may well determine the order through the scoring gate off Recife.
Once the wind begins to veer and become E or SE it is a drag race to the gate and the NE corner of Brazil and into the doldrums (ITCZ). Again there is the possibility of cutting the corner and passing close to the coast with the risk of lighter wind and a coastal effect; balanced against the longer distance but probably stronger wind out to sea. During the whole of this leg there will be squalls to dodge before the large band of clouds and squalls that mark the doldrums.
The doldrums (ITCZ) will be found near the equator. West is usually considered best when crossing the ITCZ and there will be a favourable current running across the equator to the NW. However finding the best place to cross through the ITCZ is tricky and the teams will be looking at weather models and satellite pictures to determine the best spot. But finding the best spot can be difficult as clouds build and disperse after violent squalls. Sometimes yachts within sight of each other will be split by a cloud and at the next report one will have gained 20 miles or more. So a period of calms and heavy squalls is likely before they are released into the trade winds of the northern hemisphere.
Once into the NE trades it is a drag race again close reaching with squalls to dodge in what should be champagne sailing conditions with 15 knots of wind and sunshine. The Azores (Bermudan) high will be to the north and once the racers are past the chain of Caribbean Islands they may find that the high pressure is ridging across the course towards Florida. This is an area known as the horse latitudes and is typically an area of light variable wind between the trade winds and the westerlies to the north.
Approaching Charleston the yachts pass through the Gulf Stream which is a quickly moving warm water current and is also an area where depressions form. Whilst these will usually pass to the north, aggressive cold fronts can sweep off the USA bringing a rapid swing in the wind to the NW along with gales and strong squalls. The presence of the Gulf Stream and an abundant supply of heat adds energy to the system, and what initially appears as a rather insignificant feature, can rapidly change into something more dangerous.
The outcome of the race is going to depend on a mixture of some important tactical decisions as well as straight line speed. Although a warm leg there will be some significant squalls to watch for, and how the individual yachts handle the squalls may make a big difference to the outcome. A torn sail early in the race may well be felt later on, but changing sails each time a cloud approaches is exhausting work.
Although there may be a helping hand from a cold front as the yachts leave, it is more likely that it will be a relatively slow start in a thermally driven wind and a struggle to get around Cape Frio and into the trade winds. Whoever does this the best, will get a lead that will be difficult to overcome before the scoring gate off Recife with the next passing place not until the doldrums.
www.portimaoglobaloceanrace.com/
by Oliver Dewar
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